Here's a very simple example of marshaling comparing Marshal dump and load in Ruby using YAML, vs. custom JSON marshalers: http://www.skorks.com/2010/04/serializing-and-deserializing-...

Note that the post shows a tree structure in YAML because Marshall gives it to you for free (synonymous with Java serialize behavior). But the post punts on implementing the same tree in JSON, probably because it's messy and complicated.

Nothing about that looks simple to me. For example, the JSON class label "A" has to be interpreted by something to actually instantiate an A Object. YAML is a bit better-- it at least defines that there is a Ruby class instance being marshaled -- but it doesn't help you if that class doesn't exist the same on client and server.

Pretty soon this leads to madness in production systems where the server evolves "A" (v2) among a sea of separately evolving clients "A" (v1, v1.1, v1.2). Then versioned class annotations get introduced, followed by attempts to differentiate between serializable and non-serializable fields, deep and shallow serialization, etc. etc. Pretty soon, your JSON marshaling isn't so simple anymore.